Kobo ereaders are great, when I’m on trips I download epub files on my phone, plug the ereader to my phone via USB, copy-paste the books and it just works. No need to install anything on the Kobo.

I got a kobo recently and noticed bad performance with some epubs, very slow loading times and page flips. If I convert the to kepub with calibre (requires a plugin) then it’s super fast but I don’t think there is calibre for phones.

I never had performance issues, but I don’t read huge books or anything. There seem to be some online converters, but I agree that is not the most ergonomic. Maybe calibre-web could also do the job, with you connecting to it through your phone’s browser.

Never heard about the kepub format but I’ll look into it, sounds cool.